1. Field of the Invention
The present invention relates to a telephone system used for an extension telephone system, etc., in an office. In particular, the present invention relates to a telephone system for performing voice communication among terminals by using an Internet protocol (IP).
2. Description of the Related Art
A system for communicating voice information via a best effort type communication network such as the Internet is known (for example, refer to Jpn. Pat. Appln. KOKAI Publication No. 2004-229151). The system of this type is sometimes referred to as an IP phone system or a voice over IP (VoIP). This technology is also applied to a local communication network such as a private phone network. Hereinafter, a telephone device in the system of this type is referred to as an IP phone particularly, and a system formed on the premises is referred to as a private IP phone system.
The IP is a general-purpose communication protocol in computer-to-computer communication, so that it can flexibly achieve a linkage function with a computer by using the IP phone system. In the office, with a linkage between a telephone directory system structured on a local area network (LAN) and the IP phone system, such a function of, for example, call originating from a closest extension phone terminal to an opposite party pointed on a graphical user interface (GUI) can be achieved.
To use a function of this type, it is necessary to clarify beforehand a correspondence relationship between a computer terminal operated by a user and an IP phone to be an object of call originating/incoming. The extension phone network in the office is fixedly structured to some extent. Therefore, as far as the computer terminal (desktop PC, etc.) which is not so varied in position, the correspondence relationship between the phone and the computer is easily obtained.
However, the use of an IP system extremely needs to fully take advantage of mobility to be one of its merits. With the use of a portable type computer (notebook PC, etc.) for example, it is greatly convenient, if it is possible to use the linkage function with a telephone directory by using a closest phone at any place on the premises. However, in a system in which a positional relationship between the phone and the computer terminal is frequently varied, a technique to momentarily manage the correspondence relationship of the both is not known. Therefore, it is hard to say that an existing system fully takes advantage of the IP system.
Assuming that the existing system can use the linkage function with the telephone directory, there is not much point if the operation of the linkage function is complicated. Since the linkage function is originally a function for making its operation easy, it would defeat the purpose of the linkage function if a complicated operation is required to utilize it.
A related technique is also disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-104653. In this document, an information communication system is disclosed, wherein it becomes possible for information exchange to an opposite party who is now on the phone via the Internet by a linkage operation between the phone and an electronic appliance close to the phone. However, this technique does not achieve a mutual linkage between unspecified number of phones and electronic appliances.
As mentioned above, in the existing phone system, a function to link mutual positions between the phone dice and the information terminal is not sufficient and additional improvements for the phone system are desired.